Teacher Preparation Notes for A Scientific Investigation What types of food contain starch and protein? 1

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1 Teacher Preparation Notes for A Scientific Investigation What types of food contain starch and protein? 1 In this activity, students first learn about the structure and functions of starch and protein and the role of glucose in the synthesis of starch and amino acids. Then, students learn the scientific method by carrying out key components of a scientific investigation, including: generating hypotheses developing experimental methods designing and carrying out experiments to test the hypotheses if appropriate, using experimental results to revise the hypotheses. The Student Handout provides information and questions to guide students in designing the first experiment, which evaluates two indicator solutions to see whether they can be used to test for starch or for protein. Then, students use the results from the first experiment and inductive reasoning to formulate hypotheses concerning which types of food contain starch and which types of food contain protein (some or all foods derived from animals or plants or both). Next, students use deductive reasoning based on their hypotheses to make predictions for a second experiment to test their hypotheses. Finally, students carry out the second experiment and use the results to evaluate their hypotheses and, if necessary, modify these hypotheses. Before beginning this activity, students should have a basic understanding of atoms and molecules. This activity will probably require two 50-minute laboratory periods. You may want to have a pre-laboratory discussion of the material on pages 1-3 of the Student Handout. Learning Goals In accord with the Next Generation Science Standards 2 : Students learn the Disciplinary Core Ideas: o LS1.C: Organization for Matter and Energy Flow in Organisms "The sugar molecules thus formed contain carbon, hydrogen, and oxygen; their hydrocarbon backbones are used to make amino acids and other carbon-based molecules that can be assembled into larger molecules (such as proteins or DNA), used for example to form new cells." Students engage in the Science Practices of o "Planning and carrying out investigations" Students should be able to: "Decide what data are to be gathered and how measurements will be recorded." "Decide how much data are needed to produce reliable measurements and consider any limitations on the precision of the data." "Plan experimental procedures, identifying the need for controls." o "Analyzing and interpreting data" Students should be able to: "Analyze data systematically, either to look for salient patterns or to test whether data are consistent with an initial hypothesis." "Evaluate the strength of the conclusion that can be inferred from any data set " o o constructing explanations arguing from evidence. 1 By Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania, These Teacher Preparation Notes and the related Student Handout are available at 2 Quotations are from and 1

2 This activity helps to prepare students for the Performance Expectation: o HS-LS1-6. "Construct and revise an explanation based on evidence for how carbon, hydrogen and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules." This activity can help students to understand the Crosscutting Concept, Energy and Matter. This activity helps students to understand the Nature of Science, including: o Scientific inquiry is characterized by a common set of values that include: logical thinking, precision, open-mindedness, objectivity, skepticism, replicability of results, and honest and ethical reporting of findings. o Science knowledge is based on empirical evidence. Specific Learning Goals Starch is a polymer of glucose. The function of starch is glucose storage. Proteins are polymers of 20 different types of amino acids. The many different types of proteins serve a variety of functions such as transport, motion and enzyme. In plants, photosynthesis combines CO2 and H2O to make glucose and other sugars. Glucose provides precursor molecules to make other types of plant molecules. For example, molecules derived from glucose plus NH4+ are used to make amino acids. The monomers (amino acids or glucose) are joined together to make the polymers (proteins or starch). Accurate, consistent methods and replication of experiments are needed to produce reliable experimental results. Inductive reasoning can provide useful generalizations based on specific observations, but the results of inductive reasoning should be treated with caution, since additional observations may show exceptions to a generalization. To test a hypothesis, scientists use deductive reasoning to predict specific experimental results expected on the basis of the hypothesis. Experiments to test a hypothesis often produce results that stimulate scientists to modify their original hypothesis; then scientists perform additional experiments to test their modified hypothesis. An indicator is a substance that changes color in the presence of a particular type of organic compound. To evaluate the specificity of an indicator, it is important to include negative controls. Food contains organic compounds made by plants, animals or other organisms. Starch is found in some foods derived from plants. Significant quantities of protein are found in some foods derived from animals and some foods derived from plants. Supplies Indicator Solution 1 = Iodine-Potassium Iodide Solution (~12 ml per class; available from if not in an opaque container, should be stored in the dark) Indicator Solution 2 = Biuret reagent (~50 ml per class; available from Biuret reagent should be fresh since old Biuret reagent is less sensitive as a protein indicator.) 3 3 To dispose of significant amounts of Biuret solution, do not pour into sink drains or sewers, but instead contact a permitted waste disposer. It appears that the tiny amounts of Biuret solution added to each sample can safely be disposed of by placing the tested samples in the regular trash. Additional safety information is available at and 2

3 Dropper bottles for the indicator solutions (bare minimum of two, one for each indicator solution; ideally, as many as the number of student groups in your largest class, so each pair of student groups can share a pair of dropper bottles; available from search for plastic dropping bottles) Containers for testing such as small plastic or Styrofoam cups (28 if you have containers that will be washed and reused or, if you do not have a sink, 48 per class; white containers or transparent containers placed on a white background make it easier to see the color change in the indicator solutions; small paper cups should not be used because at least some brands test positive for starch even when the sample is pure water) Markers for labeling the containers Stirrers (e.g. plastic knives and/or spoons; 1 or 2 per student group in your largest class; more if you do not want students to have to wash stirrers during the experiment) Gloves (minimum of 1 per student group per day) (Goggles can also help student safety.) If you want your students to measure the amounts of each sample, you can use milliliter pipettes to measure amounts of water and oil and a scale to measure amounts of the solid samples and egg white. However, the tests for starch and protein work well with estimated amounts of samples, and your students can use measuring spoons to measure the amounts of samples. For Part 2, students can use: o slightly less than 1/8 teaspoon of starch or sucrose, each dissolved in slightly less than ½ teaspoon of water o less than 1/16 teaspoon of gelatin, dissolved in slightly less than ½ teaspoon of water o slightly less than ¼ teaspoon of liquid egg white, oil or water. For Part 3, students can use: o 1/8 teaspoon of almond paste, mixed with slightly less than 1/8 teaspoon of water o slightly less than ¼ teaspoon of jelly, mixed with slightly less than 1/8 teaspoon of water o slightly less than ¼ teaspoon of butter and of yogurt. When you buy a set of measuring spoons, we recommend that you look for a set that includes 1/8 teaspoon measure. (In many sets ¼ teaspoon is the smallest measure.) If you have your students use measuring spoons, you should substitute the teaspoon amounts for the gram amounts on pages 4 and 6 of the Student Handout.) Samples amount needed per class for Part 2 (It will be good to have a little extra of each of these.) o Corn starch (~1.2 g or ~ ½ teaspoon; can be found in the baking needs aisle) o Potato starch (~1.2 g or ~ ½ teaspoon; can be found in the baking needs aisle) o Liquid egg whites (~3.2 g or ~1 teaspoon; an alternative is egg white from a whole egg or powdered egg whites (~1.2 g or ~ ½ teaspoon; can be found in the supplements aisle at Trader Joe s; a student group would dissolve ~0.3 g in ~2 ml of water) o Unsweetened Gelatin (~0.4 g or < ~¼ teaspoon) o Sucrose = "table sugar" (~1.2 g or ~ ½ teaspoon) o Vegetable oil (~4 ml) Samples amount needed per class for Part 3 (It will be good to have a little extra of each of these.) o Beans (~8 canned beans; we have had good success with white cannellini beans which are easy to mash and have a light color, so the color change of Biuret solution is more visible) o Almond paste (~2.5 g or ½ teaspoon; can be found in the baking needs aisle) 3

4 o Jelly (~6 g or ~1 teaspoon; since Part 2 of the activity analyzes the starch and protein content of foods derived from plants vs. animals, you will want to check the label to make sure your jelly does not contain gelatin) o Butter (~4 g or ~1 teaspoon) o Yogurt (~4 g or ~1 teaspoon; you should check the ingredients list to make sure you have a brand of yogurt (e.g. Stonyfield) that does not contain starch) Water (tap water should be fine; ~40 ml or ~9 teaspoons per class for Part 2 and ~10 ml or ~2 teaspoons per class for Part 3 + water for washing unless you have enough containers and stirrers so students do not need to wash them) Suggestions for Implementation and Discussion To maximize student participation and learning, I recommend that you have students work on groups of related questions individually or in pairs before having a class discussion of their answers. In the Student Handout, numbers in bold indicate questions for the students to answer and Ø indicates a step in the experimental procedure for the students to do. If you use the Word version of the Student Handout to make changes for your students, please check the PDF version to make sure that the figures and formatting in the Word version are displaying correctly on your computer. A key is available upon request to Ingrid Waldron (iwaldron@sas.upenn.edu). The following paragraphs provide additional instructional suggestions and background information some for inclusion in your class discussions and some to provide you with relevant background that may be useful for your understanding and/or for responding to student questions. Part 1 Introduction to Starch and Proteins The Student Handout shows the more common form of starch. The figure below shows both forms of starch. ( ) Question 2 will help students notice that starch, like other carbohydrates, contain only carbon, hydrogen and oxygen, whereas proteins also contain nitrogen. (The sulfur-containing amino acids are not mentioned in the Student Handout.) 4

5 Protein functions include: transport within the cell, across cell membranes, and in the blood (e.g. hemoglobin) movement (including cilia, flagella and muscles) structure enzymes chemical messengers (e.g. hormones) defense against infection (e.g. antibodies). If your students are not familiar with the different functions of proteins, you may want to show them the YouTube video "Protein Functions in the Body" (available at Omit the hormone section at the end, since it has inaccuracies. Page 2 of the Student Handout describes how some of the glucose molecules produced by photosynthesis are used to make starch 4 and some are used to provide carbon backbones for the synthesis of other plant molecules. The Student Handout does not describe the other major use of glucose molecules as input for cellular respiration to produce ATP, which provides energy for cellular processes. 5 The first figure on the next page shows how molecules produced during the cellular respiration of glucose are used to synthesize amino acids. Since the carbon and oxygen atoms in the sugars produced by photosynthesis are derived from CO2, the carbon skeletons used to make amino acids are also ultimately derived from CO2 from the air. 4 During the day time, much of the sugar produced by photosynthesis is converted to starch. At night, when photosynthesis is not occurring, starch is broken down and used for cellular respiration. 5 For more information, see Cellular Respiration and Photosynthesis Important Concepts, Common Misconceptions, and Learning Activities ( which includes background information and suggested learning activities for your students. 5

6 ( The nitrogen needed for amino acid synthesis is taken up by the roots. NO3- is converted to NH4+ for incorporation in amino acids. This figure summarizes nitrogen metabolism in plants. ( 6

7 Plants and bacteria can synthesize all of the amino acids they need. In contrast, humans must consume amino acids, although they can produce approximately half of the types of amino acids from other amino acids by a process called transamination, which is illustrated in the figure below. (The amino acids which our bodies cannot produce and must take in from our food are called essential amino acids.) Transamination also plays an important role in the synthesis of amino acids in prokaryotes and plants. ( ) Part 2 How can we test for starch and protein? You can either have your students measure the amount of each sample and water precisely or just estimate the approximate amount (estimates can work equally well; see page 3 of these Teacher Preparation Notes for additional information). To evaluate whether each indicator solution is a good indicator for starch or for protein, students should look for color changes when the indicator is added to: more than one type of starch more than one type of protein negative controls, including water, sugar and oil. The negative controls are important to establish that an indicator solution shows color change only for starch or only for protein. The expected results are that, in the presence of starch, iodine will change color from yellow-brown to blue-black, and, in the presence of protein, Biuret reagent will turn from blue to purple. Biuret reagent is a little less reliable than the iodine indicator; it is important to use fresh Biuret reagent and it would be good to double check this test yourself ahead of time. You may want to show your students the color change for each of the indicator solutions before they begin their testing, so they will know what to look for. This will be helpful, for example, so students do not confuse the slight color change when egg whites are mixed with iodine with the reaction that occurs if starch is present. To accomplish the goals of having negative controls and replicating results, the experimental design should have duplicate tests with each indicator for each sample for a total of 2 replicates x 2 indicator solutions x 7 samples = 28 tests. I suggest that you have your students work in groups of 2-4, and have replicate tests done by different groups (so whatever experimental error one group might make won't affect the replicate test). To maintain student engagement, you may want to have each student group test a starch sample, a protein sample, and one of the negative controls with each indicator. For example, if you have six student groups, you could use the following plan. Group Samples to Be Tested 1 corn starch, egg whites, sucrose 2 potato starch, gelatin, vegetable oil 3 corn starch, gelatin, water 4 potato starch, egg whites, water 5 corn starch, egg whites, vegetable oil 6 potato starch, gelatin, sucrose 7

8 This would result in three replicates of each starch and protein sample and two replicates of each negative control. To accommodate this plan, you will probably want to substitute the following table for the table currently shown on the top of page 5 of the Student Handout. You may want to display this table on the board, so each student group can enter their data. Sample Corn Starch Potato starch Egg whites Gelatin Sucrose Vegetable oil Water Did indicator solution 1 change color? Did indicator solution 2 change color? Replicate 1 Replicate 2 Replicate 3 Replicate 1 Replicate 2 Replicate 3 Question 9 can be used to introduce the advantages of replication of each test. You may want to introduce the concept of false positives (which could occur if there were contamination) and false negatives (which could result from insufficient amounts of sample and/or indicator solution). Also, if there is only a small color change, this may be interpreted as a positive response by some observers, but not others. If there are any differences between replicate tests, you may want to lead a class discussion of methodological factors that may have influenced the test results. The test should be repeated with optimum methodology to resolve the conflict. You can point out to your students that an important and necessary part of scientific research is to refine and standardize methods in order to get consistent and reliable results. In discussing questions 11c and 12c, you will want to include the limitations of inductive reasoning (see e.g. especially when only a limited number of samples have been tested. To be more certain of conclusions concerning whether either of these indicator solutions can be used to test for starch or for protein, it would be desirable to test each indicator solution on a wider variety of samples, including additional types of starch and protein, as well as glucose and amino acids (the monomers of starch and protein, respectively). Part 3 What types of food contain starch? What types of foods contain protein? In this part, students: first use the data from Part 1 to generate hypotheses about what types of food contain starch and protein, then carry out experiments to test these hypotheses, interpret the results to see whether they support the hypotheses, and, if the initial hypotheses were not supported or only partially supported, formulate new revised hypotheses. You will probably want to point out to your students that this is how real scientists work as they develop progressively better understanding of a research question. 8

9 Student hypotheses in response to question 14 will probably vary. This provides the opportunity to mention that this type of disagreement also happens in "real science" when different scientists have different interpretations of the same evidence; typically, these disagreements are resolved by obtaining additional evidence. At this point, all student hypotheses should be accepted as legitimate hypotheses to be tested by further experimentation, provided the hypotheses are compatible with the results from Part 2 which should show that: Some, but not all, foods derived from plants contain starch. At least some foods derived from animals do not contain starch. At least some foods derived from animals contain protein. At least some foods derived from plants do not contain protein. Some of the student hypotheses may provide the opportunity to discuss how people formulate hypotheses based on both the results of the current experiment and also prior knowledge; this can be a useful part of the scientific process and contribute to cumulative improvements in our understanding of scientific questions. To test these hypotheses, students will need to do replicate tests for each of the samples listed in question 15 with each of the indicator solutions. Thus, you will want a total of 5 samples x 2 indicator solutions x 2 replicates = 20 tests. In interpreting the results of their tests, students should be aware that their tests may not be sensitive enough to detect small amounts of starch or protein. The level of protein is high enough to be easily detected in concentrated sources of protein such as egg whites, beans or milk (where it provides nutrition for the growing bird embryo, plant seedling, or baby mammal, respectively). You may want to discuss how scientific results are sometimes ambiguous, and scientists try to improve their methodology and repeat the experiment to clarify any ambiguity. Comparing the results of testing the samples in Part 2 vs. Part 3 for protein demonstrates the risk of generalizing from a limited set of observations. In Part 2 none of the foods derived from plants and all of the foods derived from animals have significant amounts of protein, but in Part 3 beans and almond paste have a significant amount of protein and butter has almost no protein (so little that it is not detectable with our test). You may want to point out that generating the hypotheses in question 14 requires inductive reasoning (generalizing from specific examples to more general hypotheses, which has the risk of overgeneralizing, as demonstrated in this activity), whereas making the predictions in question 15 requires deductive reasoning (reasoning from general hypotheses to specific predictions, often used to test hypotheses). Only plants produce starch, but starch is not present in significant amounts in some foods derived from plants, because the food is derived from a part of the plant that has little or no starch and/or because preparation of the food product has removed starch that was initially present. In plants, starch can be broken down to glucose and used for cellular respiration to produce ATP. Molecules that can be used for cellular respiration are stored in glycogen in animals and fat in animals and seeds (where the greater amount of energy per unit of weight in fat is useful for mobility). 9

10 Professional nutritional analysis provides the following values for starch and protein content for the food samples in this activity (% by weight; = missing data). Food Starch Protein Corn starch ~91% 0% Potato starch Liquid egg whites 0% 11% Powdered egg whites 81% Gelatin, unsweetened 0% 86% Sucrose 0% 0% Vegetable oil (corn oil) 0% 0% White beans (canned) 7% Kidney beans (canned) 9% 5% Almond paste 0% 10% Jellies 0% Butter 0% 1% Low-fat vanilla yogurt * 0% 5% (Most data from accessed in 2012) * These figures apply to brands like Stonyfield which do not add starch; read the ingredients list in the label to purchase a type of yogurt which does not have starch added. Additional Resources for Teaching about the Scientific Method A wealth of resources for teaching and understanding the scientific process are provided in "Understanding Science How science really works", available at "Using the Scientific Method" (available at is a simulation of a simple experiment with questions to guide the students in describing and analyzing their simulated experiment; the simulation can be carried out quickly, so students can spend most of their time on learning about important issues in experimental design and interpretation, including the need to have all variables except the experimental variable the same for the control and experimental groups in order to test the effect of the experimental variable. "The Strange Case of Beri beri" (available at "Battling Bad Science" is an entertaining talk about the errors and deceptions behind misleading nutritional or medical advice, available at (the first 7.5 minutes are the most relevant). Additional Hands-on Activities in Which Students Design Experiments and Interpret the Results: Activities that are explicitly aligned with the Next Generation Science Standards are indicated by (NGSS). "Enzymes Help Us Digest Food", available at 10

11 Students learn about enzyme function, enzyme specificity and the molecular basis of lactose intolerance through experiments with the enzyme lactase and analysis and discussion questions. Students engage in the scientific practices of designing and carrying out experiments and interpreting data. (NGSS) Homeostasis and Negative Feedback Concepts and Breathing Experiments This minds-on, hands-on activity begins with analysis and discussion questions that develop student understanding of homeostasis and negative feedback, the difference between negative and positive feedback, and the cooperation between the respiratory and circulatory systems to provide O2 and remove CO2 for cells all over the body. Then, students carry out and analyze an experiment which investigates how rate and depth of breathing are affected by negative feedback regulation of blood levels of CO2 and O2. Finally, students formulate a question concerning effects of exercise on breathing, design and carry out a relevant experiment, analyze and interpret their data, and relate their results to homeostasis during exercise. (NGSS) "Regulation of Human Heart Rate", available at Students learn how to measure heart rate accurately. Then students design and carry out an experiment to test the effects of an activity or stimulus on heart rate, analyze and interpret the data, and present their experiments in a poster session. "Moldy Jell-O", available at Students design experiments to determine how substrate and environmental conditions influence growth of common molds. Students carry out their experiments, analyze and interpret their evidence, and prepare a report. Discussion Activities for Learning about the Process of Science "Carbohydrate Consumption, Athletic Performance and Health Using Science Process Skills to Understand the Evidence", available at This analysis and discussion activity is designed to develop students' understanding of the scientific process by having them design an experiment to test a hypothesis, compare their experimental design with the design of a research study that tested the same hypothesis, evaluate research evidence concerning two hypothesized effects of carbohydrate consumption, evaluate the pros and cons of experimental vs. observational research studies, and finally use what they have learned to revise a standard diagram of the scientific method to make it more accurate, complete and realistic. "Vitamins and Health Why Experts Disagree", available at In this analysis and discussion activity, research concerning the health effects of vitamin E is used as a case study to help students understand why different research studies may find seemingly opposite results. Students learn useful approaches for evaluating and synthesizing conflicting research results, with a major focus on understanding the strengths and weaknesses of different types of studies (laboratory experiments, observational studies, and clinical trials). Students also learn that the results of any single study should be interpreted with caution, since results of similar studies vary (due to random variation and differences in specific study characteristics). Sources for Figures in Student Handout 11

12 Starch Amino acids and Protein mages/figure1.png 12